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184_notes:current [2018/05/15 15:11] – curdemma | 184_notes:current [2021/06/08 00:45] (current) – schram45 |
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Sections 17.5 and 18.2 in Matter and Interactions (4th edition) | Sections 17.5 and 18.2 in Matter and Interactions (4th edition) |
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[[184_notes:defining_current|Previous Page: Defining Current]] | /*[[184_notes:resistors|Next Page: Resistors]] |
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| [[184_notes:defining_current|Previous Page: Defining Current]]*/ |
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===== Current in Wires ===== | ===== Current in Wires ===== |
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==== Drift speed in wire ==== | ==== Drift speed in wire ==== |
{{ 184_notes:vdrift.png?200}} | [{{ 184_notes:vdrift.png?200|Graph of electron speed in a wire vs time}}] |
Modeling all of these interactions for every electron in the electron current is quite complicated (or almost impossible). While there are several ways to model the electrons in the wire, we will use a model called the [[https://en.wikipedia.org/wiki/Drude_model|Drude Model]], which builds off of the idea that the electrons are interacting or bouncing off the positive nuclei in the wire. In this model, the electron will experience short periods of acceleration from the electric field, followed by periods where the electron drastically slows because of collision with a positive nuclei in the wire. The average speed of the electron in this stop/start motion is called the **drift velocity**, and we say that the electron "drifts" through the metal. The drift velocity of electrons in a wire is actually quite slow compared to the speed of the individual electrons (the same way that the wind has slow speed compared to the speed of the individual air molecules). | Modeling all of these interactions for every electron in the electron current is quite complicated (or almost impossible). While there are several ways to model the electrons in the wire, we will use a model called the [[https://en.wikipedia.org/wiki/Drude_model|Drude Model]], which builds off of the idea that the electrons are interacting or bouncing off the positive nuclei in the wire. In this model, the electron will experience short periods of acceleration from the electric field, followed by periods where the electron drastically slows because of collision with a positive nuclei in the wire. The average speed of the electron in this stop/start motion is called the **drift velocity** which has units of m/s, and we say that the electron "drifts" through the metal. The drift velocity of electrons in a wire is actually quite slow compared to the speed of the individual electrons (the same way that the wind has slow speed compared to the speed of the individual air molecules). |
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Using the Drude Model, we can find the average drift velocity for the electrons in the wire. Starting with the momentum principle, we know | Using the Drude Model, we can find the average drift velocity for the electrons in the wire. Starting with the momentum principle, we know |
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====Examples==== | ====Examples==== |
[[:184_notes:examples:Week6_drift_speed|Drift Speed in Different Types of Wires]] | * [[:184_notes:examples:Week6_drift_speed|Drift Speed in Different Types of Wires]] |
| * Video Example: Drift Speed in Different Types of Wires |
[[:184_notes:examples:Week6_node_rule|Application of Node Rule]] | * [[:184_notes:examples:Week6_node_rule|Application of Node Rule]] |
| * Video Example: Application of Node Rule |
| {{youtube>cxSQbMLoUk4?large}} |
| {{youtube>NFl0ZuWfkBc?large}} |